Prommegger was too strong as he held off compatriot Lukas Mathies to win the final in comfortable fashion in Italy.
Third was Vic Wild, the youngster surprising Italy's Roland Fischnaller in the small final.
But the day belonged to Prommegger, the 32-year-old scooping the ninth World Cup win of his career.
In the women's race, Japan's Tomoka Takeuchi was the victor with Canada's Caroline Calve second and Germany's Anke Karstens third.
The defending World Cup champion Patrizia Kummer was left disappointed after the Swiss star went out in the last 16.